Greenfield is a city in Greenfield Township, Adair County, Iowa, United States. It is the county seat of Adair County. The current courthouse, which sits in the middle of the Greenfield Square, was built in 1891 and is listed on the National Register of Historic Places. Greenfield is home to the Iowa Aviation Museum and Hall of Fame. According to the United States Census Bureau, the city has a total area of 1.8 square miles (4.7 Square Kilometer), all of it land.